Mechanical, electrochemical (EIS), and microstructural characterization of reinforced concrete incorporating natural volcanic pozzolan

Abstract

The primary objective of this study was to assess the benefits of incorporating higher NMP content as a cement substitute in mortar and concrete mixtures. Our aim was to quantify and elucidate the impact of Natural Moroccan Pozzolanic material (NMP) on compressive strength, insulation performance, and corrosion resistance of reinforced concrete when exposed to chloride attack. Higher NMP dosages were considered for both economic and environmental reasons. Notably, this study is the first of its kind to focus on NMP as a cement substitute. In this study, we investigated the performance of reinforced concrete containing varying percentages of NMP as a partial substitution for Portland Cement (PC), ranging from 10% to 50% by weight. We evaluated the corrosion behavior of reinforced concrete in an aggressive medium (3% sodium chloride) after 3 and 90 days using electrochemical impedance spectroscopy (EIS). We also assessed chloride permeability by measuring the degree of chloride penetration. Additionally, we conducted microstructural characterization using Scanning Electron Microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy to analyse the impact of NMP incorporation into concrete. The study's findings revealed that a partial substitution of cement with up to 50% NMP in concrete can be achieved without compromising overall strength. The highest compressive and bending strengths were observed in mixes with a 30% replacement of cement with NMP. The increased silica, alumina, and calcium content of NMP led to the formation of new calcium silicate hydrates (CSH) and calcium alumino silicate hydrates (CASH) gels, including tobermorite and Al-tobermorite, due to a pozzolanic reaction. Furthermore, the use of NMP in concrete construction improved thermal properties, reducing heat transfer and enhancing thermal comfort. Electrochemical impedance spectroscopy (EIS) and Open Circuit Potential (OCP) results indicated that the addition of natural Moroccan pozzolan enhanced the corrosion resistance of reinforced concrete exposed to 3% NaCl medium. Additionally, the incorporation of NMP significantly reduced cement usage, aligning with sustainable development goals by lowering CO2 emissions.